The present invention generally relates to a power saving processing method and system in data processors and, more particularly, to a power saving processing method and system which detects a key input ready condition or mode independently of an application program and suitably lowers the frequency of the CPU clock in the key input ready mode.
Data processing systems for lowering the frequency of a clock signal to thereby realize a reduction of power consumption are disclosed in a paper titled "THE MACINTOSH PORTABLE" Macworld, November 1989, as well as in U.S. Pat. Nos. 4,727,491 (Culley) and 4,835,681 (Culley), and JP-A-Nos. 63-292312 and 61-43344.
Among data processing systems, most small-sized data processing systems such as personal computers are designed to be operated with battery power from the viewpoint of its portability. Such a small data processing system is required to minimize the power consumption of constituent elements of the processor for realizing power saving and for achieving a long operating time based on the battery.
As a useful one of such conventional power saving techniques, it is known to lower the frequency of a CPU clock. This power saving system is based on reducing the frequency of the CPU clock while an application program is not executing data processing. More in detail, a clock down instruction is previously written in the application program. A CPU, when detecting the clock down instruction during the execution of the application program, lowers the frequency of the CPU clock. Under this condition, no data processing is carried out. When receiving a key input from a keyboard, the CPU increases the clock frequency again to the original level to restart the data processing.
The aforementioned prior art technique requires the analysis of the application program and the writing operation of the clock down instruction in the part of the program which is regarded as a non-data-processing part through the analysis. In other words, such modifying operation is necessary for all the application programs to be used. In addition, when the application program is not subjected to such modification as mentioned above, even the execution of the program will cause no clock down condition.